.container{
    margin: 0 auto;
    width: 900px;
    height: 1000px;
}

.fixed-box{
    width: 200px;
    height: 100px;
    background-color: lightcoral;
    position: fixed;
}
.fixed-left{
    top: 20px;
    left: 20px;
}

.fixed-right{
    top: 20px;
    right: 20px;
}